Humans have five senses—sight, smell, taste, touch, and hearing—that help them gather and interpret information about their environment. Sharks have these senses as well as others (see Figure below). Of their five basic senses, smell plays the largest role, and hearing plays the smallest. Sharks smell by detecting molecules in the water, similar to the way air-breathing vertebrates detect odor molecules. The sense of smell in sharks is so keen that they can distinguish one drop of blood in 25 gallons (115 l) of water. Some species have sensory barbels near their mouths that can pick up tastes in the seawater.
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| Typical shark external anatomy is displayed by the dogfish shark. Special sensory structures include the lateral line and the ampullae of Lorenzini, located inside the snout. |
After a shark senses prey, it homes in by traveling up the prey’s “smell corridor,” moving side to side to read clues in the water. As the shark gets closer, the corridor of clues narrows. Once the prey is found, the shark grabs it, unhinging its jaw if necessary to get its mouth around large animals. Since prey thrash around and can injure their attackers, some sharks have special nictitating membranes, thick films that cover their eyes during the final moments of the attack.
Lateral lines are sense organs located along the sides of the shark body that can detect vibrations in water. Short tubes connect the lateral lines, which are made of fluid-filled canals just under the skin, to external pores. When vibrations in water strike the pores, the lateral lines detect them, providing sharks with information about their source. Vibrations could indicate anything from a school of fish to a wounded animal.
Shark snouts possess receptors called ampullae of Lorenzini that can sense electrical energy. The cells of the receptors are sensitive enough to pick up the very small electrical impulses produced by nerves of living things. The receptors work with the nervous system to help sharks find prey that are buried in sediment or wandering out of sight in the open sea. Like all of the shark’s senses, the ampullae of Lorenzini are supported
by, and themselves support, the other sensory organs. Input from all of the shark’s senses give the animal a clear picture of everything in its environment.